In certain branches of the military, suicide rates have almost doubled in the last decade — a trend many have attributed to multiple deployments. But now, sweeping new research published in the journal JAMA Psychiatry suggests that the reasons are much more complicated than just deployment.

In a comprehensive new study that looked at all 3.9 million members of the U.S. military from 2001-2007—including the Air Force, Army, Army National Guard, Army Reserve. Marine Corps and Navy—suicide was not associated with deployment in the U.S.’s two most recent major conflicts: Operation Enduring Freedom and Operation Iraqi Freedom.

Those findings may be counterintuitive, says study author Mark A. Reger, PhD, Deputy Director at the National Center for Telehealth and Technology and chief of research, outcomes, and investigations, but some interesting theories have emerged.

“It was certainly intuitive as the wars went on and suicides went up for people to assume that deployment was the reason, but our data show that that is too simplistic; when you look at the total population, deployment is not associated with suicide,” Reger toldReuters.

The strongest research from the Vietnam and Gulf War eras shows there’s not a significant difference in suicide rates between those who are deployed and the general population, he says. And that held true for the more recent conflicts. The authors looked at deployment in the Iraq and Afghanistan operations and found no association between deployment and suicide.

They suspect part of the reason is that military members who are chosen for deployment may be among the most mentally fit. Prior to deployment, all service members go through pre-deployment screening to ensure that they’re mentally and physically ready for the challenges.

“Those who really struggle with a deployment don’t go the second time,” Dr. Alan Peterson, a psychologist at the University of Texas Health Science Center in San Antonio who specializes in combat-related post traumatic stress disorder (PTSD), toldReuters. “Early separation from the military is often a marker for something else.”

The researchers didn’t look at data related to mental health status, medical status, combat exposure or combat injuries, so they were unable to confirm if those factors were linked to increase suicide risk, though they plan to do more research in that area in the future. “We also would like to look at factors such as combat exposure — obviously everyone who deploys does not see the same level of combat, and that may have an impact, as do combat injuries or other factors,” Reger told the Military Times.

Some patterns linked to suicide risk factors did emerge, however. Those who left the military early had a 63% higher suicide rate than people who had not separated from service. People with the fewest years of military service were also most at risk; service members who left the military after just a short stint of less than four years were at higher risk for suicide than those who left after serving four or more years, regardless of whether or not they’d been deployed.

The study didn’t look at possible reasons for this, but the authors speculate that difficulty finding work, losing their military identity and having to find new social support may all play a role. “Additional research is needed to clarify what the circumstances are surrounding early discharges and how these factors may be related to suicide,” the authors wrote.

Another big risk factor, the study authors concluded, was the nature of a service member’s discharge. Those who were not honorably discharged from the military had a 21% higher suicide rate than those who had an honorable discharge.

Making use of limited resources to prevent suicide is a key objective of the military, Reger says. Based on these findings, it’s possible that targeting prevention efforts more narrowly to those who leave the military early and those with a less-than-honorable discharge may be more efficient and impactful than casting a wide net and focusing prevention efforts on everyone who’s deployed, Reger says.

As the Military Times points out, all Iraq and Afghanistan veterans are eligible for up to five years of medical care through the VA if they have been discharged under “other-than-dishonorable conditions,” but those who received a dishonorable or bad-conduct discharge may not be eligible for those benefits. Based on the new findings, Reger suggests it may be helpful to offer suicide prevention options for those who have discharges that were not honorable.

Importantly, said Reger, the findings could also clear up misconceptions about military veterans. “It can be a disservice to service members to misrepresent the nature of the population,” he said. “We need to be clear that the deployed force overall adjusts well and is not at increased for suicide.”